In recent years, flat electric storage cells having a substantially rectangular planar shape, such as a lithium ion secondary battery or an electric double layer capacitor, have been put to practical use, and are regarded as promising as a power source for various equipment because of their high energy density, miniaturizability, easy maintenance, and the like.
Such planar electric storage cells are often used as an assembled cell that is packaged by laminating a plurality of the electric storage cells. When the electric storage cells are installed on a hybrid electric vehicle, an electric vehicle, or the like as a power source, it is necessary to ensure their durability to withstand vibrations.
For example, Japanese Unexamined Patent Application Publication No. 2003-157813 discloses a technique for increasing the vibration-isolation effect of an assembled cell by preventing an external case that is a support member for unit cells from reaching a resonance point in a real usage region, by shifting a natural frequency of the assembled cell to the higher frequency side.
When the planar electric storage cells are packaged, there is a case where individual electric storage cells are each accommodated in a frame body, and a plurality of the frame bodies each having accommodated the electric storage cell is constituted as an assembled cell. In this case, in accommodating the planar cell into the frame body, it is possible to adopt, for example, a structure wherein one frame body is divided into two members, and after the two members have been opposed to each other, a storage portion of the electric storage cell and a sealing portion are clamped by pressing them planarly.
However, in such a structure in which all electric storage cells are planarly fixed, the size of the package increases by a space for fixing the sealing portion, and in addition, there is a possibility that the storage portion with a relatively large weight and the sealing portion with a relatively light weight will move at mutually different frequencies or amplitudes from each other, so that a stress might concentrate on the boundary portion between the storage portion and the sealing portion, resulting in a reduced durability. In particular, when the thickness of the storage portion and that of the sealing portion vary due to dimension deviations among individual electric storage cells, it is impossible to clamp the storage portion and the sealing portion by simultaneously pressing them, leading to a reduction in shock resistance.
The present invention has been made in view of the above-described circumstances. The object of the present invention is to provide a package structure of electric storage cells, the package structure being capable of increasing the shock resistance of the electric storage cells while downsizing the package.